In wireless communication networks, techniques are used to account for errors in packets or lost packets that are transmitted from one wireless communication device to another wireless communication device. One technique is to retransmit a packet when it is not received or when it is received with so many errors that it cannot be corrected using an error correction technique at the receiving device. A retransmission of a packet is generally to be avoided when possible because it makes for inefficient use of the communication channel.
Hybrid Automatic Repeat Request (HARQ or Hybrid ARQ) is an example of a retransmission scheme in which information blocks (packets) are encoded at a transmitting device for partial error correction at the receiving device, and when the receiving device indicates that it cannot correct certain errors, the transmitting device retransmits the portion of the original transmission that the receiving device could not correct.
Any performance gain that can be achieved using HARQ techniques has tradeoffs. The benefits of retransmission schemes such as HARQ techniques are that the retransmission and combination of transmissions reduces the fading margin requirement and packet error rates. In a consistent wireless channel environment, HARQ can be used to boost the modulation and coding schemes that can be used for the transmissions. However, HARQ can also reduce the transmission efficiency inherently caused by retransmissions. Even though the use of HARQ may allow for a higher modulation and coding scheme, too many retransmissions may have the overall effect of reducing total throughput.